The present invention generally relates to fluid control valves. More particularly, this invention relates to a fast-acting fluid control valve capable of opening and closing more quickly that conventional valves of comparable flow capacity as a result of reduced moving mass, decreased stroke distance, and increased actuator properties, which preferably include reduced magnetic diffusion time (less lag before activation/deactivation) and increased force to mass ratio.
Research efforts have been made to design fluid control valves with rapid opening and closing speeds. Examples include U.S. Pat. Nos. 6,105,616 and 6,474,353 to Sturman et al., which disclose a valve with two connected flow paths defined at the outer circumferential surface of a solid spool (plunger). The spool is contained and axially movable within a valve housing. The spool has a central axial hole, conferring a generally tubular shape to the spool, to prevent fluid from being trapped between the ends of the spool and the housing and exerting a counteracting static force on the spool. While the spool is capable of rapidly opening and closing in part due to the very small size of the spool, speed is limited by inherent eddy currents in the spool and the relatively large mass of the spool resulting from its relatively thick wall. The extent to which the thickness of the spool wall can be reduced is limited by hoop stresses, since all fluid pressure is exerted on the exterior of the spool.
Another example of a rapid-actuated valve is disclosed in U.S. Pat. No. 7,077,378 to Rampen et al., which notably differs from the valve taught by Sturman et al. by having an annular-shaped spool (sealing ring) that is axially actuated by a combination of magnets (permanent and/or electromagnetic) and optionally springs. Flow is axial over the inner and outer circumferential surfaces of the spool, thereby avoiding the effect of hoop stresses on the structural integrity of the spool. Because flow is entirely in the axial direction, the shape of the spool must be carefully tailored so that closure of the spool against axially spaced seats occurs while maintaining approximately equal flow velocities at the inner and outer circumferential surfaces of the spool. Nonetheless, the spool is a check valve that cannot open against very high pressures because it is not axially balanced.
Notwithstanding the above, further improvements in valve performance, and particularly speed for a given flow rate capacity, would be desirable.